In data communication systems, such as a Digital Subscriber Line (DSL) system, a burst of known data (often called synchronization data) is typically transmitted regularly in middle of data transmission. The synchronization data is typically used to adjust and tune transceiver parameters. The synchronization data may not carry useful information and is typically considered to be part of overhead. Therefore, it is desirable to transmit this data as infrequently as possible. However, because of the variation in the communication channel and also in the transceivers themselves, it is desirable to have synchronization data as frequently as possible to adapt and retrain and retune the DSL system to the current characteristics of channel and transceivers.
The rate by which synchronization data is transmitted is usually fixed during data communication. It is usually selected such that it allows fast adaptation to changes in the communication system. This results in excessive overhead if the communication system does not change rapidly. In particular, the synchronization data is often transmitted periodically with a predetermined, fixed period. This causes inefficiency in the use of resources when the change in communication system is very slow.